The present invention relates to a method of preventing a vehicle in a starting maneuver from rolling in a direction opposite to a direction selected to move the vehicle during the starting maneuver, wherein brake force is built up and/or maintained on at least one wheel brake during standstill of the vehicle.
The invention further relates to a device that is appropriate to implement the method.
Starting maneuver assist systems are known by the name ‘hill holder’ or the name Hill Start Assist (HSA) that will be used in the following, wherein the driver of a vehicle is assisted in a starting maneuver on a slope by a method of the type initially referred to.
It is usually provided that a service brake system of the vehicle is equipped with an energy supply unit, by means of which a defined brake pressure is automatically built up in one or more wheel brakes of the vehicle, or a brake pressure set by the driver in one or more wheel brakes is maintained in order to keep the vehicle in a standstill position until a starting maneuver of the vehicle is detected. Alternatively, it can be arranged that brake force is generated during standstill by means of an externally controllable parking brake device, which is released during the starting maneuver.
It is decisive in the HSA function that, during the starting maneuver, the brake force is neither reduced too early, whereby the vehicle could roll back, nor too late, with the result that the traction force would be reduced when starting to drive, what the driver perceives as a loss in dynamics.
It is known in this respect to reduce the brake force during a starting maneuver corresponding to a balancing of torques of downhill, brake and engine drive torques that act on a wheel of the vehicle, as has been described in European patent EP 1 023 547 B1. It is necessary, however, to determine the drive torque or the parameters decisive for the control of the brake force reduction by way of an engine model. To this end, engine performance characteristics must be recorded for each engine-gearbox variation of a vehicle, and the parameters must be adapted to the respective engine performance characteristics, for which purpose a repeated test and adaptation is generally required.
This procedure is very time-consuming, which is a major problem in view of the fact that frequently relative short times are only available for the development. In addition, it is customary that the engine performance characteristics are also adapted in the current series, what could cause mistuning of the HSA and necessitate an adaptation of the HSA, respectively.
Further, it has frequently been found in the known procedure that brake force is reduced too early or too late so that the vehicle rolls back in a starting maneuver or the dynamics in starting is impaired. Due to the necessary individual adaptation of the parameters to the various engine-gearbox variations of a type of vehicle, very different starting performances have been encountered in different variations in addition, what is not desirable in a series vehicle.
In view of the above, an object of the invention is to further improve upon a method of the above-mentioned type in such a way that the previously required expenditure in time for the adaptation of a starting aid is reduced. Another objective of the invention relates to disclosing a device that is suitable to implement the method.